California Vehicle Code section 22658
(h) A towing company may impose a charge of not more than one-half of the regular towing charge for the towing of a vehicle at the request of the owner, the owner's agent, or the person in lawful possession of the private property pursuant to this section if the owner of the vehicle or the vehicle owner's agent returns to the vehicle after the vehicle is coupled to the tow truck by means of a regular hitch, coupling device, drawbar, portable dolly, or is lifted off the ground by means of a conventional trailer, and before it is removed from the private property. The regular towing charge may only be imposed after the vehicle has been removed from the property and is in transit.